Ringed airfoil with mixing elements

ABSTRACT

A shrouded fluid turbine includes a ringed airfoil having a leading edge, a trailing edge, an outer surface, an inner surface, and a body extending from the leading edge to the trailing edge. The shrouded turbine further includes a rotor surrounded by the ringed airfoil. The rotor is disposed downstream of the leading edge and about a central axis of the fluid turbine. The shrouded turbine further includes an aperture extending through the body of the ringed airfoil between the outer surface and the inner surface. The aperture is configured to mix a first fluid flow adjacent to the outer surface of the ringed airfoil and a second fluid flow downstream of the rotor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/622,078, entitled “RING AIRFOIL WITH MIXING ELEMENTS” and filed on Apr. 10, 2012, which is hereby incorporated by reference in its entirety.

BACKGROUND

Conventional horizontal axis wind turbines (HAWTs) used for power generation have one to five open blades having a rotor, attached at a hub and arranged like a propeller, the blades being mounted to a horizontal shaft attached to a gear box which drives a power generator. The gearbox and generator equipment are housed in a nacelle.

Diffusor augmented wind turbines (DAWT) are well known to increase the amount of energy that a given wind turbine rotor can extract from a fluid stream. In a ducted turbine the upstream area of the fluid stream is larger than the area at the rotor plane due to the flow contraction at the duct. The fluid stream is contracted at the rotor plane by the duct and expands after leaving the duct. The energy that may be harvested from the fluid is proportional to the upstream area where the fluid stream starts in a non-contracted state. In a conventional diffuser augmented turbine the diffuser surrounds the rotor such that the diffuser guides incoming fluid prior to the fluid interaction with the rotor, providing the greatest unit-mass flow rate substantially proximal to the rotor plane.

Annular airfoils used in ducted fluid turbines have an inlet or leading edge and an exit or trailing edge with the lift or suction side of the airfoils on the side proximal to the rotor. The fluid stream is divided into a low pressure, high velocity stream on the interior side of the airfoil, and a high pressure, lower velocity stream on the exterior of the airfoil. The high pressure, lower velocity stream is the bypass flow.

Duct augmented wind turbines often employ bypass ducts or multi-element annular airfoils for preventing flow separation from the interior of the duct. Introducing a relatively small volume of bypass flow to the turbine wake is sufficient to maintain flow attachment over the interior surface of the duct. A mixer ejector turbine introduces a relatively greater volume of bypass flow into the wake of the turbine for extracting more energy at the rotor.

Ejectors are fluid jet pumps that draw flow into a system and thereby increase the flow rate through that system. Mixer-ejectors may be generally approximated as short compact versions of such jet pumps that are relatively insensitive to incoming flow conditions, and have been used, for instance, on aircraft for providing propulsion in high speed jet propulsion applications involving flow velocities near or above the speed of sound. See, for example, U.S. Pat. No. 5,761,900 by Dr. Walter M. Presz, Jr., which uses a mixer downstream to increase thrust while reducing noise from the discharge. Dr. Presz is a co-inventor in the present application.

SUMMARY

In accordance with an example embodiment, a fluid turbine system includes a substantially ringed airfoil with mixing elements surrounding a rotor. In some embodiments, the fluid turbine system may further include ejector elements forming a mixer-ejector pump that provides an increased unit mass flow rate at the rotor plane, when compared to ambient or bypass flow, and rapidly mixes the low energy turbine exit flow with high energy bypass flow near the exit of the system.

According to another example embodiment a ringed airfoil includes one or more mixing elements along the trailing edge of the ringed airfoil, forming a mixer augmented turbine (MAT). A MAT mixes fluid passing through the rotor with fluid that bypasses the shrouded rotor. The portion of the ambient fluid stream that flows outside of the ringed airfoil is referred to as bypass flow. The bypass flow has greater energy content than that of the fluid stream that has passed through the rotor and had energy extracted from it. Introducing bypass flow into the region downstream of the rotor plane is referred to as “energizing the wake,” which provides reduced pressure behind the rotor plane, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. In some embodiments the MAT may further include at least one ejector element. The MAT provides a means of energizing the wake behind the rotor plane. The combination of the effects of the mixing elements and the energized wake provide a rapidly-mixed, shorter wake compared to the wake of horizontal axis wind turbines with open rotors.

According to an embodiment, a shrouded fluid turbine includes a ringed airfoil having a leading edge, a trailing edge, an outer surface, an inner surface, and a body extending from the leading edge to the trailing edge. The shrouded turbine further includes a rotor surrounded by the ringed airfoil. The rotor is disposed downstream of the leading edge and about a central axis of the fluid turbine. The shrouded turbine further includes an aperture extending through the body of the ringed airfoil between the outer surface and the inner surface. The aperture is configured to mix a first fluid flow adjacent to the outer surface of the ringed airfoil and a second fluid flow downstream of the rotor.

In some embodiments, the aperture may include one end disposed downstream of the rotor. In some embodiments, the shrouded fluid turbine may further include a plurality of mixing elements disposed on the trailing edge of the ringed airfoil. Each of the mixing elements may be configured to further mix the first fluid flow adjacent to the outer surface of the ringed airfoil and the second fluid flow downstream of the rotor. In some embodiments, at least one of the mixing elements may extend downstream of the rotor. In some embodiments, at least one of the mixing elements may include a converging portion extending toward the central axis. In some embodiments, at least one of the mixing elements may include a diverging portion extending away from the central axis. In some embodiments, at least one of the mixing elements may include a converging portion extending toward the central axis and a diverging portion extending away from the central axis.

In some embodiments, a first one of the mixing elements may include a converging portion extending toward the central axis and a second one of the mixing elements may include a diverging portion extending away from the central axis. The fluid turbine may further include an ejector element disposed on the ringed airfoil proximal to a radial plane such that the ejector element is in fluid communication with the first one of the mixing elements. The radial plane may extend outwardly from the central axis and pass through the first one of the mixing elements. The ejector element may be configured to further mix the first fluid flow adjacent to the outer surface of the ringed airfoil and the second fluid flow downstream of the rotor. In some embodiments, at least a portion of the ejector element may include a surface of the second one of the mixing elements.

In some embodiments, at least one of the mixing elements may be disposed on the inner surface of the ringed airfoil and may include a converging portion extending toward the central axis, and an ingress aperture adjacent to the inner surface of the ringed airfoil and configured to receive at least a portion of a third fluid flow adjacent to the inner surface. In some embodiments, at least one of the mixing elements may be configured to direct the received portion of the third fluid flow away from the inner surface.

In some embodiments, a first one of the mixing elements may include a converging portion extending toward the central axis and a second one of the mixing elements may include a diverging portion extending away from the central axis. The fluid turbine may further include an ejector element disposed on the ringed airfoil proximal to a radial plane such that the ejector element is in fluid communication with the second one of the mixing elements. The radial plane may extend outwardly from the central axis and pass through the second one of the mixing elements. The ejector element may be configured to further mix the first fluid flow adjacent to the outer surface and the second fluid flow downstream of the rotor.

In some embodiments, the ringed airfoil may further include a faceted trailing edge. In some embodiments, the ringed airfoil may further include an outer surface and an inner surface. The faceted trailing edge may be configured to mix, downstream of the rotor, a first fluid flow adjacent to the outer surface of the ringed airfoil and a second fluid flow adjacent to the inner surface of the ringed airfoil. In some embodiments, the faceted trailing edge may include a facet extending away from the central axis. In some embodiments, the shrouded fluid turbine may further include an ejector element disposed on the facet such that the ejector element is in fluid communication with the facet. In some embodiments, the ejector element may be configured to mix, downstream of the rotor, the first fluid flow adjacent to the outer surface of the ringed airfoil and the second fluid flow adjacent to the inner surface of the ringed airfoil.

According to an embodiment, a shrouded fluid turbine includes a ringed airfoil including a leading edge, a trailing edge, an outer surface and an inner surface, and a rotor surrounded by the ringed airfoil. The rotor is disposed downstream of the leading edge and about a central axis of the fluid turbine. The shrouded fluid turbine further includes a plurality of mixing elements disposed on the trailing edge of the ringed airfoil. Each of the mixing elements is configured to mix a first fluid flow adjacent to the outer surface and a second fluid flow downstream of the rotor. The shrouded fluid turbine further includes a set of ejector elements disposed downstream of the rotor and at least partially surrounded by the ringed airfoil. The set of ejector elements includes a converging portion extending toward the central axis and a diverging portion extending away from the central axis. Each of the ejector elements is configured to mix a first portion of the second fluid flow downstream of the rotor and a second portion of the second fluid flow downstream of the rotor.

In some embodiments, at least one of the mixing elements may extend downstream of the rotor. In some embodiments, at least one of the mixing elements may include a converging portion extending toward the central axis. In some embodiments, at least one of the mixing elements may include a diverging portion extending away from the central axis.

According to an embodiment, a shrouded fluid turbine includes a ringed airfoil having a leading edge, a trailing edge, an outer surface, an inner surface, and a body extending from the leading edge to the trailing edge. The shrouded fluid turbine further includes a rotor surrounded by the ringed airfoil. The rotor is disposed downstream of the leading edge and about a central axis of the fluid turbine. The shrouded fluid turbine further includes a plurality of mixing elements disposed on the trailing edge of the ringed airfoil. Each of the mixing elements is configured to further mix a first fluid flow adjacent to the outer surface of the ringed airfoil and a second fluid flow downstream of the rotor. The shrouded fluid turbine further includes a first one of the mixing elements including a converging portion extending toward the central axis, a second one of the mixing elements including a diverging portion extending away from the central axis, and an ejector element disposed on the ringed airfoil proximal to a radial plane such that the ejector element is in fluid communication with the second one of the mixing elements. The radial plane extends outwardly from the central axis and passes through the second one of the plurality of mixing elements. The ejector element is configured to further mix the first fluid flow adjacent to the outer surface and the second fluid flow downstream of the rotor.

In some embodiments, at least one of the mixing elements extends downstream of the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings, which are presented for the purposes of illustrating the disclosure set forth herein and not for the purposes of limiting the same. The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 2 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 3 is a rear, right, perspective view of the example embodiment of FIG. 2.

FIG. 4 is a side, orthographic, section view of the embodiment of FIGS. 2 and 3.

FIG. 5 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 6 is a rear, right, perspective view of the example embodiment of FIG. 5.

FIG. 7 is a side, orthographic, section view of the embodiment of FIGS. 5 and 6.

FIG. 8 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 9 is a rear, right, perspective view of the example embodiment of FIG. 8.

FIG. 10 is a side, orthographic, section view of the embodiment of FIGS. 8 and 9.

FIG. 11 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 12 is a rear, right, perspective view of the example embodiment of FIG. 11.

FIG. 13 is a side, orthographic, section view of the embodiment of FIGS. 11 and 12.

FIG. 14 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 15 is a rear, right, perspective view of the example embodiment of FIG. 14.

FIG. 16 is a side, orthographic, section view of the embodiment of FIGS. 14 and 15 illustrating a cut through the converging mixing element.

FIG. 17 is a side, orthographic, section view of the embodiment of FIGS. 14 and 15 illustrating a cut through the diverging mixing element.

FIG. 18 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 19 is a rear, right, perspective view of the example embodiment of FIG. 18.

FIG. 20 is a side, orthographic, section view of the embodiment of FIGS. 18 and 19.

FIG. 21 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 22 is a rear, right, perspective view of the example embodiment of FIG. 21.

FIG. 23 is a side, orthographic, section view of the embodiment of FIGS. 21 and 22 illustrating a cut through the converging mixing element.

FIG. 24 is a side, orthographic, section view of the embodiment of FIGS. 21 and 22 illustrating a cut through the diverging mixing element.

FIG. 25 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 26 is a rear, right, perspective view of the example embodiment of FIG. 25.

FIG. 27 is a side, orthographic, section, detail view of the embodiment of FIGS. 25 and 26.

FIG. 28 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 29 is a rear, right, perspective view of the example embodiment of FIG. 28.

FIG. 30 is a side, orthographic, section, detail view of the embodiment of FIGS. 28 and 29.

FIG. 31 is a front, right, perspective view of an example embodiment of the present disclosure.

FIG. 32 is a rear, right, perspective view of the example embodiment of FIG. 31.

FIG. 33 is a side, orthographic, section, detail view of the embodiment of FIGS. 31 and 32.

DETAILED DESCRIPTION

A more complete understanding of the components, processes, and apparatuses disclosed herein can be obtained by reference to the accompanying figures. These figures are intended to demonstrate the present disclosure and are not intended to show relative sizes and dimensions or to limit the scope of the example embodiments.

Although specific terms are used in the following description, these terms are intended to refer only to particular structures in the drawings and are not intended to limit the scope of the present disclosure. It is to be understood that like numeric designations refer to components of like function.

The term “about” when used with a quantity includes the stated value and also has the meaning dictated by the context. For example, it includes at least the degree of error associated with the measurement of the particular quantity. When used in the context of a range, the term “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the range “from about 2 to about 4” also discloses the range “from 2 to 4.”

A turbine including a substantially ringed airfoil with mixing elements, in accordance with various embodiments, provides an improved means of extracting energy from fluid currents. Some embodiments include ejector elements providing a mixer/ejector pump. The substantially ringed airfoil surrounds a rotor, which extracts power from a primary fluid stream. The substantially ringed airfoil, mixing elements and, in some embodiments, ejector elements draw more flow through the rotor allowing more energy extraction due to higher flow rates. The MAT transfers energy from the bypass flow to the rotor wake flow allowing higher energy per unit mass flow rate through the rotor. These two effects enhance the overall power production of the turbine system. As used herein, reference to a “substantially ringed airfoil” or a “ringed airfoil” may be used interchangeably and are not intended to be limiting in scope. The present disclosure contemplates an airfoil that may be primarily ring shaped without interruption or may have regions where the airfoil has gaps and/or deviations in shape from the circular (e.g., substantially ringed) shape.

The term “rotor” is used herein to refer to any assembly in which one or more blades are attached to a shaft and able to rotate, allowing for the extraction of power or energy from wind rotating the blades. Example rotors include a propeller-like rotor or a rotor/stator assembly. Any type of rotor may be enclosed within the turbine shroud in the wind turbine of the present disclosure.

The leading edge of a ringed airfoil may be considered the front of the fluid turbine, and the trailing edge of a ringed airfoil or ejector element may be considered the rear of the fluid turbine. A first component of the fluid turbine located closer to the front of the turbine may be considered “upstream” of a second component located closer to the rear of the turbine. Put another way, the second component is “downstream” of the first component.

In an example embodiment, a fluid turbine includes a ringed airfoil that surrounds a rotor and includes mixing elements. In another example embodiment, the ringed airfoil includes ejector elements that are disposed on an outer surface of the ringed airfoil and/or mixing elements.

FIG. 1 is a perspective view of an example embodiment 100 of a shrouded turbine. Referring to FIG. 1 the turbine 100 includes a substantially ringed airfoil 110, a nacelle body 150, a rotor 140, and mixing elements including converging mixing elements 117 that turn inwardly toward a central axis 105, and diverging mixing elements 115 that turn outwardly from the central axis 105. The substantially ringed airfoil 110 includes a front end 112, also known as an inlet end or a leading edge. Mixing elements form a rear end 116, also known as an exhaust end or trailing edge. Support structures 106 are engaged at the proximal end with the nacelle 150 and at the distal end with the ringed airfoil 110. The rotor and hub 140, nacelle 150 and mixing elements 115, 117 are concentric about the central axis 105 and are supported by a tower structure 102. The location of the mixing elements 115, 117 at the trailing edge of the substantially ringed airfoil 110 is solely for ease in describing the example embodiment, and is not intended to be limiting in scope. In accordance with other aspects of the present disclosure, the mixing elements 115, 117 may be positioned at any location on the surfaces of the substantially ringed airfoil 110.

FIG. 2 is a front perspective view of an example embodiment 200 of a shrouded turbine. FIG. 3 is a rear perspective view of the embodiment 200 of FIG. 2. FIG. 4 is a side, orthographic, section view of the embodiment 200 of FIG. 2 taken along a line 2-2. The shrouded turbine 200 includes a ringed airfoil 210 with bypass apertures or passages 219. The ringed airfoil 210 includes a leading edge 212 and a trailing edge 216. A body of the airfoil 215 extends from the leading edge 212 to the trailing edge 216. Each aperture 219 extends from an outer surface 206 of the body 215 and through the body 215 to an inner surface 207 of the body 215. In some embodiments, one end 222 of the aperture 219 is located downstream of the rotor plane 209, although it will be understood that in other embodiments the end 222 of the aperture 219 may be located elsewhere along the inner surface 207 of the body 215, such as upstream of the rotor plane 209. In some embodiments, the apertures 219 can be located at regular intervals around the ringed airfoil 210.

A bypass flow, represented by arrow 203, passes from the exterior of the body 215 through each aperture 219 to the region downstream of the rotor plane 209. Each aperture 219 provides mixing of the bypass flow 203, flowing adjacent to the outer surface 206, with a fluid stream, represented by arrow 204, flowing adjacent to the inner surface 207 in the region downstream of the rotor 140, also referred to as the rotor wake. The aperture 219 may be referred to as a bypass duct. The ringed airfoil 210 and apertures 219 transfer energy from the bypass flow 203 to the fluid stream 204. The bypass flow 203 has greater energy content than that of the fluid stream 204 that has passed through the rotor and had energy extracted from it by the generator (not shown). Introducing the bypass flow 209 into the region downstream of the rotor plane 209 provides reduced pressure behind the rotor plane 209, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 140, which enhances the overall power production of the shrouded turbine 200.

FIG. 5 and FIG. 6 are front and rear perspective views, respectively, of an example embodiment 300 of a shrouded turbine. FIG. 7 is a side, orthographic, section view of the embodiment 300 of FIG. 5 taken along a line 5-5. The shrouded turbine 300 includes a ringed airfoil 310 with converging mixing elements 317 and apertures or passages 319. The ringed airfoil 310 includes a leading edge 312 and a trailing edge 316. A body of the airfoil 315 extends from the leading edge 312 to the trailing edge 316. The trailing edge 316 includes the converging mixing elements 317 having inner surfaces 318 exposed to a fluid stream 304 and outer surfaces 320 covered by the body 315. The converging mixing elements 317 include a portion that extends inwardly toward the central axis 305 of the rotor 140. Each aperture 319 extends from an outer surface 306 of the body 315 and through the body 315 to an inner surface 307 of the body 315. In some embodiments, one end 322 of the aperture 319 is located downstream of the rotor plane 309, although it will be understood that in other embodiments the end 322 of the aperture 319 may be located elsewhere along the inner surface 307 of the body 315, such as upstream of the rotor plane 309. In some embodiments, the apertures 319 can be located at regular intervals around the ringed airfoil 310.

A bypass flow, represented by arrow 303, passes from the exterior of the body 315 through each aperture 319 to the region downstream of the rotor plane 309. The converging mixing elements 317 and the apertures 319 provide mixing of the bypass flow 303, flowing adjacent to the outer surface 306, with a fluid stream, represented by arrow 304, flowing adjacent to the inner surface 307 in the region downstream of the rotor 140, also referred to as the rotor wake. The aperture 319 may be referred to as a bypass duct. The ringed airfoil 310, including the converging mixing elements 317 and apertures 319 transfer energy from the bypass flow 303 to the fluid stream 304. The bypass flow 303 has greater energy content than that of the fluid stream 304 that has passed through the rotor and had energy extracted from it by the generator (not shown). Introducing the bypass flow 309 into the region downstream of the rotor plane 309 provides reduced pressure behind the rotor plane 309, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 140, which enhances the overall power production of the shrouded turbine 300.

FIG. 8 and FIG. 9 are front and rear perspective views, respectively, of an example embodiment 400 of a shrouded turbine. FIG. 10 is a side, orthographic, section view of the embodiment 400 in FIG. 8 taken along a line 8-8. The shrouded turbine 400 includes a ringed airfoil 410 with converging mixing elements 417, diverging mixing elements 415 and bypass apertures or passages 419. The ringed airfoil 410 includes a leading edge 412 and a trailing edge 416. The trailing edge 416 includes the converging mixing elements 417 having inner surfaces 418 extending inwardly toward the central axis 405 of the rotor 140. The inner surfaces 418 are exposed to a fluid stream 404. The trailing edge 416 further includes the diverging mixing elements 415 extending outwardly away from the central axis 405. Each aperture 419 extends from an outer surface 406 of the diverging mixing elements 415 and through the diverging mixing elements 415 to an inner surface 407 of the diverging mixing elements 415. In some embodiments, one end 422 of the aperture 419 is located downstream of the rotor plane 409, although it will be understood that in other embodiments the end 422 of the aperture 419 may be located elsewhere along the inner surface 407 of the diverging mixing elements 415, such as upstream of the rotor plane 409. In some embodiments, the converging mixing elements 417, diverging mixing elements 415 and apertures 419 can be located at regular intervals around the ringed airfoil 410.

A bypass flow, represented by arrow 403, passes from the exterior of the diverging mixing elements 415 through the apertures 419 to the region downstream of the rotor plane 409. The converging mixing elements 417, diverging mixing elements 415 and the apertures 419 provide mixing of the bypass flow 403, flowing adjacent to the outer surface 406, with a fluid stream, represented by arrow 404, flowing adjacent to the inner surface 407 in the region downstream of the rotor 140, also referred to as the rotor wake. The aperture 419 may be referred to as a bypass duct. The ringed airfoil 410 and apertures 419 transfer energy from the bypass flow 403 to the fluid stream 404. The bypass flow 403 has greater energy content than that of the fluid stream 404 that has passed through the rotor and had energy extracted from it by the generator (not shown). Introducing the bypass flow 409 into the region downstream of the rotor plane 409 provides reduced pressure behind the rotor plane 409, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 140, which enhances the overall power production of the shrouded turbine 400.

FIG. 11 and FIG. 12 are front and rear perspective views of an example embodiment 500 of a shrouded turbine. FIG. 13 is a side, orthographic, section view of the embodiment 500 in FIG. 11 taken along a line 11-11. The shrouded turbine 500 includes a ringed airfoil 510 with converging mixing elements 517. The ringed airfoil 510 includes a leading edge 512 and a trailing edge 516. The trailing edge 516 includes the converging mixing elements 517 having inner surfaces 518 extending inwardly toward the central axis 505 of the rotor 140. In some embodiments, the converging mixing elements 417 can be located at regular intervals around the ringed airfoil 410.

Converging mixing elements 517 are looped forms that engage with the trailing edge of the ringed airfoil 515 and have a leading edge 528 and a trailing edge 531. An ingress aperture 519 in the loop form of the converging mixing elements 517, adjacent to an interior surface 507 of the ringed airfoil 510, pulls laminar flow away from the trailing edge 516 and promotes mixing vortices at the exit of the ringed airfoil 510. The fluid stream through the inlet 512 of the ringed airfoil flows along the inner surface of the airfoil and divides into a first fluid stream 530 that remains attached to the airfoil and a second fluid stream 532 that is diverted by mixing element 517. Dividing the first fluid stream 530 and the second fluid stream 532 into the region downstream of the rotor plane 509 provides reduced pressure behind the rotor plane 509, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 140, which enhances the overall power production of the shrouded turbine 500.

FIG. 14 and FIG. 15 are front and rear perspective views, respectively, of an example embodiment 600 of a shrouded turbine. FIG. 16 is a side, orthographic, section view of the embodiment 600 in FIG. 14 taken along a line 14-14 cut through a converging mixing element 617. FIG. 17 is a side, orthographic, section view of the embodiment 600 in FIG. 14 taken along a line 14′-14′ cut through a diverging mixing element 615. The shrouded turbine 600 includes a ringed airfoil 610 with converging mixing elements 617 and diverging mixing elements 615 as well as bypass apertures or passages 619 and ejector elements 627. The ringed airfoil 610 includes a leading edge 612 and a trailing edge 616. The trailing edge 616 includes the converging mixing elements 617 extending inwardly toward from the central axis 605 and the diverging mixing elements 615 extending outwardly away from the central axis 605. At least one aperture 619 allows the introduction of bypass fluid flow 603 to enter the exiting stream behind the rotor plane 609. Each aperture 619 extends through the diverging mixing elements 615. In some embodiments, one end of the aperture 619 is located downstream of the rotor plane 609, although it will be understood that in other embodiments the end of the aperture 619 may be located elsewhere, such as upstream of the rotor plane 609.

Additional bypass flow 604 is introduced to the fluid stream downstream from the rotor by at least one ejector element 627. Each ejector element 627 is mounted on the ringed airfoil 610 and is proximal to the same radial plane as the corresponding converging mixing elements 617. In other words, the ejector element 627 is proximal to the converging mixing elements 617 and is in fluid communication with the corresponding converging mixing element 617, and is not in fluid communication with the diverging mixing elements 615. In some embodiments, the converging mixing elements 617, diverging mixing elements 615, apertures 619 and ejector elements 627 can be located at regular intervals around the ringed airfoil 610. For example, the converging mixing elements 617 and the diverging mixing elements 615 may be alternately located adjacent to each other on the ringed airfoil 610.

The bypass flow, represented by arrow 603, passes from the exterior of the diverging mixing elements 615 through the apertures 619 to the region downstream of the rotor plane 609. The converging mixing elements 617, diverging mixing elements 615 and the apertures 619 provide mixing of the bypass flow 603 and 604 with a fluid stream flowing in the region downstream of the rotor 140, also referred to as the rotor wake. The aperture 619 may be referred to as a bypass duct. The ringed airfoil 610, apertures 619 and ejector elements 627 transfer energy from the bypass flow 603 and 604 to the fluid stream. The bypass flow 603 and 604 has greater energy content than that of the fluid stream that has passed through the rotor and had energy extracted from it by the generator (not shown). Introducing the bypass flow 603 and 604 into the region downstream of the rotor plane 609 provides reduced pressure behind the rotor plane 609, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 140, which enhances the overall power production of the shrouded turbine 600.

FIG. 18 and FIG. 19 are front and rear perspective views, respectively, of an example embodiment 700 of a shrouded turbine. FIG. 20 is a side, orthographic, section view of the embodiment 700 in FIG. 18 taken along a line 18-18 cut through a diverging mixing element 715. The shrouded turbine 700 includes a ringed airfoil 710 with converging mixing elements 717 and diverging mixing elements 715 as well as ejector elements 727. The ringed airfoil 710 includes a leading edge 712 and a trailing edge 716. The trailing edge 716 includes the converging mixing elements 717 extending inwardly toward from the central axis 705 and the diverging mixing elements 715 extending outwardly away from the central axis 705.

A bypass flow 704 is introduced to the fluid stream downstream from the rotor by at least one ejector element 727. Each ejector element 727 is mounted on the ringed airfoil 710 and is proximal to the same radial plane as the corresponding diverging mixing elements 715. In other words, the ejector element 727 is proximal to the corresponding diverging mixing element 715 and is in fluid communication with the corresponding diverging mixing element 715, and is not in fluid communication with the converging mixing elements 717. In some embodiments, the converging mixing elements 717, diverging mixing elements 715 and ejector elements 727 can be located at regular intervals around the ringed airfoil 710. For example, the converging mixing elements 717 and the diverging mixing elements 715 may be alternately located adjacent to each other on the ringed airfoil 710.

The ringed airfoil 710 and ejector elements 727 transfer energy from the bypass flow 704 to the fluid stream. The bypass flow 704 has greater energy content than that of the fluid stream that has passed through the rotor and had energy extracted from it by the generator (not shown). Introducing the bypass flow 704 into the region downstream of the rotor plane 709 provides reduced pressure behind the rotor plane 709, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 140, which enhances the overall power production of the shrouded turbine 700.

FIG. 21 and FIG. 22 are front and rear perspective views, respectively, of an example embodiment 800 of a shrouded turbine. FIG. 23 is a side, orthographic, section view of the embodiment 800 in FIG. 21 taken along a line 21-21 cut through the diverging mixing element 815. FIG. 24 is a side, orthographic, section view of the embodiment 800 in FIG. 21 taken along a line 21′-21′ cut through the converging mixing element 817. The shrouded turbine 800 includes a ringed airfoil 810 with converging mixing elements 817 and diverging mixing elements 815 as well as bypass ducts or passages 819. The ringed airfoil 810 includes a leading edge 812 and a trailing edge 816. The trailing edge 816 includes the converging mixing elements 817 and the diverging mixing elements 815. Each aperture 819 extends through the ringed airfoil 810 and allow the introduction of bypass fluid flow 804 to enter the exiting stream behind the rotor plane 809 (FIG. 23). Additional bypass flow 803 is introduced to the downstream flow by the ejector elements 827. Each ejector element 827 includes a leading edge 828 and a trailing edge 829. The ejector element leading edge 828 is formed by the shape of the cut in the ringed airfoil 810. The body of the ejector element airfoil section 827 includes a portion of the diverging mixing element 815. The trailing edge of the mixing element 831 includes a shared trailing edge 816 of the ringed airfoil 810. Each ejector element 827 is proximal to the same radial plane as the corresponding converging mixing element 817. In other words, each ejector element 827 is in fluid communication with the corresponding converging mixing elements 817 and shares an upper outer surface with diverging mixing elements 815, and does not engage with the inner surface of diverging mixing elements 815.

The ringed airfoil 810, converging mixing elements 817, diverging mixing elements 815 and ejector elements 827 transfer energy from the bypass flow 803 and 803 to the fluid stream passing through the rotor 140. The bypass flow 804 has greater energy content than that of the fluid stream that has passed through the rotor 140 and had energy extracted from it by the generator (not shown). Introducing the bypass flow 804 into the region downstream of the rotor plane 809 provides reduced pressure behind the rotor plane 809, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 140, which enhances the overall power production of the shrouded turbine 800.

FIG. 25 and FIG. 26 are front and rear perspective views, respectively, of an example embodiment 900 of a shrouded turbine. FIG. 27 is a side, orthographic, section view of the embodiment 900 in FIG. 25 taken along a line 23-23 cut through a diverging mixing element 915. The shrouded turbine 900 includes a ringed airfoil 910 with converging mixing elements 917 and diverging mixing elements 915 as well as a set of ejector elements 960 located downstream of the rotor 140, on the interior of the ringed airfoil 910, providing turbulent mixing and a low pressure region, downstream from the rotor plane 909. The ringed airfoil 910 includes a leading edge 912 and a trailing edge 916. The trailing edge 916 includes the converging mixing elements 917 and the diverging mixing elements 915. The set of ejector elements 960 is proximal to the nacelle 950 and is downstream of the rotor 140. The ejector elements 960 allow the introduction of bypass fluid flow 903 to enter the exiting stream behind the rotor plane 909 (FIG. 27). Additional mixing flow 907 is introduced to the downstream flow by converging ejector elements 927, which extend inwardly toward the central axis 905, and diverging ejector elements 925, which extend outwardly from the central axis 905. The set of ejector elements 960 include a leading edge 922, the diverging ejector element 925 and the converging ejector element 927, and a trailing edge 929. The leading edge 922 of the diverging ejector elements 925 includes a two sided airfoil, and the diverging ejector elements 925 include a narrow pressure side airfoil shape, also known as a one-sided airfoil. A one-sided airfoil located on the interior of the ringed airfoil 910 provides the benefits of ejector elements, such as low pressure behind the rotor and additional wake mixing, without the mass or side wind loads that an ejector located on the outside of the ringed airfoil.

FIG. 28 and FIG. 29 are front and rear perspective views, respectively, of an example embodiment 1000 of a shrouded turbine. FIG. 30 is a side, orthographic, section view of the embodiment 1000 in FIG. 28 taken along a line 28-28 cut through the center of a faceted segment 1015. The ringed airfoil 1010 includes a substantially annular leading edge 1012 and a trailing edge 1016 as well as apertures or passages 1019 that provide mixing between bypass flow 1003 and the fluid stream downstream from the rotor plane 1009. The trailing edge 1016 includes a faceted perimeter with nodes 1017 and facets 1015. The faceted trailing edge 1016 provides stream-wise mixing. Each aperture 1019 extends from an outer surface 1006 of the ringed airfoil 1010 and through to an inner surface 1007 of the ringed airfoil 1010. In some embodiments, one end 1022 of the aperture 1019 is located downstream of the rotor plane 1009, although it will be understood that in other embodiments the end 1022 of the aperture 1019 may be located elsewhere along the inner surface 1007 of the ringed airfoil 1010, such as upstream of the rotor plane 1009. In some embodiments, the apertures 1019 can be located at regular intervals around the ringed airfoil 1010. The apertures 1019 allow the introduction of bypass fluid flow 1003 to enter the exiting stream behind the rotor plane 1009 (FIG. 30).

A bypass flow, represented by arrow 1003, passes from the exterior of the ringed airfoil 1010 through the apertures 1019 to the region downstream of the rotor plane 1009. Each aperture 1019 provides mixing of the bypass flow 1003, flowing adjacent to the outer surface 1006, with a fluid stream flowing adjacent to the inner surface 1007 in the region downstream of the rotor 1040, also referred to as the rotor wake. The aperture 1019 may be referred to as a bypass duct. The ringed airfoil 1010 and apertures 1019 transfer energy from the bypass flow 1003 to the fluid stream. The bypass flow 1003 has greater energy content than that of the fluid stream that has passed through the rotor and had energy extracted from it by the generator (not shown). Introducing the bypass flow 1003 into the region downstream of the rotor plane 1009 provides reduced pressure behind the rotor plane 1009, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 1040, which enhances the overall power production of the shrouded turbine 1000.

FIG. 31 and FIG. 32 are front and rear perspective views, respectively, of an example embodiment 1100 of a shrouded turbine. FIG. 33 is a side, orthographic, section view of the embodiment 1100 in FIG. 31 taken along a line 31-31 cut through the center of a faceted segment 1115. A ringed airfoil 1110 includes a substantially annular leading edge 1112 as well as apertures or passages 1119 that provide mixing between bypass flow 1003, 1004 and the fluid stream downstream from the rotor plane 1109. The ringed airfoil 1110 includes a leading edge 1112 and a trailing edge 1116. The trailing edge 1116 includes a faceted perimeter with nodes 1117 and facets 1115. Each aperture 1119 allows the introduction of bypass fluid flow 1103 to enter the exiting stream behind the rotor plane 1109 (FIG. 33). Additional bypass flow 1104 is introduced to the downstream flow by each of the ejector elements 1127. The additional bypass flow 1104 flows through an opening between each ejector element 1127 and each corresponding facet 1115. Each ejector element 1127 includes a leading edge 1128 and a trailing edge 1129 and is mounted on the ringed airfoil proximal to the same radial plane as the respective facet 1115. In other words, each ejector element 1127 is proximal to the facets 1115 and is in fluid communication with the corresponding facets 1115. In some embodiments, the apertures 1119 and ejector elements 1129 can be located at regular intervals around the ringed airfoil 1110. For example, the apertures 1119 and ejector elements 1129 may be located adjacent to each other on the ringed airfoil 1110.

The bypass flow, represented by arrow 1103, passes from the exterior of the ringed airfoil 1110 through the apertures 1119 to the region downstream of the rotor plane 1109. Each aperture 1119 provides mixing of the bypass flow 1103 with a fluid stream flowing in the region downstream of the rotor 1140, also referred to as the rotor wake, and each ejector element 1127 provides mixing of the bypass flow 1104 with the fluid stream flowing in the region downstream of the rotor 1140. The aperture 1119 may be referred to as a bypass duct. The ringed airfoil 1110, apertures 1119 and ejector elements 1127 transfer energy from the bypass flow 1103 and 1104 to the fluid stream. The bypass flow 1103 and 1104 has greater energy content than that of the fluid stream that has passed through the rotor and had energy extracted from it by the generator (not shown). Introducing the bypass flow 1103 and 1104 into the region downstream of the rotor plane 1109 provides reduced pressure behind the rotor plane 1109, and accordingly increased fluid velocity at the cross sectional area of the rotor plane. This allows a higher energy per unit mass flow rate through the rotor 1140, which enhances the overall power production of the shrouded turbine 1100.

Having thus described several example embodiments of the disclosure, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Accordingly, the foregoing description and drawings are by way of example only. 

What is claimed is:
 1. A shrouded fluid turbine comprising: a ringed airfoil having a leading edge, a trailing edge, an outer surface, an inner surface, and a body extending from the leading edge to the trailing edge; a rotor surrounded by the ringed airfoil, the rotor being disposed downstream of the leading edge and about a central axis of the fluid turbine; and an aperture extending through the body of the ringed airfoil from the outer surface to the inner surface, the aperture disposed in the body to mix a first fluid flow adjacent to the outer surface of the ringed airfoil and a second fluid flow downstream of the rotor.
 2. The shrouded fluid turbine of claim 1, wherein the aperture comprises one end disposed downstream of the rotor.
 3. The shrouded fluid turbine of claim 1, further comprising a plurality of mixing elements disposed on the trailing edge of the ringed airfoil, each of the plurality of mixing elements being configured to further mix the first fluid flow adjacent to the outer surface of the ringed airfoil and the second fluid flow downstream of the rotor.
 4. The shrouded fluid turbine of claim 3, wherein at least one of the plurality of mixing elements extends downstream of the rotor.
 5. The shrouded fluid turbine of claim 3, wherein at least one of the plurality of mixing elements comprises a converging portion extending toward the central axis.
 6. The shrouded fluid turbine of claim 3, wherein at least one of the plurality of mixing elements comprises a diverging portion extending away from the central axis.
 7. The shrouded fluid turbine of claim 3, wherein at least one of the plurality of mixing elements comprises a converging portion extending toward the central axis and a diverging portion extending away from the central axis.
 8. The shrouded fluid turbine of claim 3: wherein a first one of the plurality of mixing elements comprises a converging portion extending toward the central axis, wherein a second one of the plurality of mixing elements comprises a diverging portion extending away from the central axis, and wherein the fluid turbine further comprises an ejector element disposed on the ringed airfoil proximal to a radial plane such that the ejector element is in fluid communication with the first one of the plurality of mixing elements, the radial plane extending outwardly from the central axis and passing through the first one of the plurality of mixing elements, the ejector element being configured to further mix the first fluid flow adjacent to the outer surface of the ringed airfoil and the second fluid flow downstream of the rotor.
 9. The shrouded fluid turbine of claim 8, wherein at least a portion of the ejector element comprises a surface of the second one of the plurality of mixing elements.
 10. The shrouded fluid turbine of claim 3, wherein at least one of the plurality of mixing elements is disposed on the inner surface of the ringed airfoil and comprises: a converging portion extending toward the central axis; and an ingress aperture adjacent to the inner surface of the ringed airfoil and configured to receive at least a portion of a third fluid flow adjacent to the inner surface.
 11. The shrouded fluid turbine of claim 10, wherein the at least one of the plurality of mixing elements is configured to direct the received portion of the third fluid flow away from the inner surface.
 12. The shrouded fluid turbine of claim 3: wherein a first one of the plurality of mixing elements comprises a converging portion extending toward the central axis, wherein a second one of the plurality of mixing elements comprises a diverging portion extending away from the central axis, and wherein the fluid turbine further comprises an ejector element disposed on the ringed airfoil proximal to a radial plane such that the ejector element is in fluid communication with the second one of the plurality of mixing elements, the radial plane extending outwardly from the central axis and passing through the second one of the plurality of mixing elements, the ejector element being configured to further mix the first fluid flow adjacent to the outer surface and the second fluid flow downstream of the rotor.
 13. The shrouded fluid turbine of claim 1, wherein the ringed airfoil further comprises a faceted trailing edge.
 14. The shrouded fluid turbine of claim 13, wherein the ringed airfoil further comprises an outer surface and an inner surface, and wherein the faceted trailing edge is configured to mix, downstream of the rotor, a first fluid flow adjacent to the outer surface of the ringed airfoil and a second fluid flow adjacent to the inner surface of the ringed airfoil.
 15. The shrouded fluid turbine of claim 13, wherein the faceted trailing edge comprises a facet extending away from the central axis.
 16. The shrouded fluid turbine of claim 15, further comprising an ejector element disposed on the facet such that the ejector element is in fluid communication with the facet.
 17. The shrouded fluid turbine of claim 15, wherein the ejector element is configured to mix, downstream of the rotor, the first fluid flow adjacent to the outer surface of the ringed airfoil and the second fluid flow adjacent to the inner surface of the ringed airfoil.
 18. A shrouded fluid turbine comprising: a ringed airfoil having a leading edge, a trailing edge, an outer surface and an inner surface; a rotor surrounded by the ringed airfoil, the rotor being disposed downstream of the leading edge and about a central axis of the fluid turbine; a plurality of mixing elements disposed on the trailing edge of the ringed airfoil, each of the plurality of mixing elements being configured to mix a first fluid flow adjacent to the outer surface and a second fluid flow downstream of the rotor; and a set of ejector elements disposed downstream of the rotor and at least partially surrounded by the ringed airfoil, the set of ejector elements comprising a converging portion extending toward the central axis and a diverging portion extending away from the central axis, each of the ejector elements being configured to mix a first portion of the second fluid flow downstream of the rotor and a second portion of the second fluid flow downstream of the rotor.
 19. The shrouded fluid turbine of claim 18, wherein at least one of the plurality of mixing elements extends downstream of the rotor.
 20. The shrouded fluid turbine of claim 18, wherein at least one of the plurality of mixing elements comprises a converging portion extending toward the central axis.
 21. The shrouded fluid turbine of claim 18, wherein at least one of the plurality of mixing elements comprises a diverging portion extending away from the central axis.
 22. A shrouded fluid turbine comprising: a ringed airfoil having a leading edge, a trailing edge, and an outer surface; a rotor surrounded by the ringed airfoil, the rotor being disposed downstream of the leading edge and about a central axis of the fluid turbine; a plurality of mixing elements disposed on the trailing edge of the ringed airfoil, each of the plurality of mixing elements being configured to further mix a first fluid flow adjacent to the outer surface of the ringed airfoil and a second fluid flow downstream of the rotor, a first one of the plurality of mixing elements comprising a converging portion extending toward the central axis, a second one of the plurality of mixing elements comprising a diverging portion extending away from the central axis; and an ejector element disposed on the ringed airfoil proximal to a radial plane such that the ejector element is in fluid communication with the second one of the plurality of mixing elements, the radial plane extending outwardly from the central axis and passing through the second one of the plurality of mixing elements, the ejector element being configured to further mix the first fluid flow adjacent to the outer surface and the second fluid flow downstream of the rotor.
 23. The shrouded fluid turbine of claim 22, wherein at least one of the plurality of mixing elements extends downstream of the rotor. 